Deferred Shading - Disadvantages

Disadvantages

One key disadvantage of deferred rendering is the inability to handle transparency within the algorithm, although this problem is a generic one in Z-buffered scenes and it tends to be handled by delaying and sorting the rendering of transparent portions of the scene. Depth peeling can be used to achieve order-independent transparency in deferred rendering, but at the cost of additional batches and g-buffer size. Modern hardware, supporting DirectX 10 and later, is often capable of performing batches fast enough to maintain interactive frame rates. When order-independent transparency is desired (commonly for consumer applications) deferred shading is no less effective than forward shading using the same technique.

Another serious disadvantage is the difficulty with using multiple materials. It's possible to use many different materials, but it requires more data to be stored in the G-buffer, which is already quite large and eats up a large amount of the memory bandwidth.

One more rather important disadvantage is that, due to separating the lighting stage from the geometric stage, hardware anti-aliasing does not produce correct results any more: although the first pass used when rendering the basic properties (diffuse, normal etc.) can use anti-aliasing, it's not until full lighting has been applied that anti-alias is needed. One of the usual techniques to overcome this limitation is using edge detection on the final image and then applying blur over the edges, however recently more advanced post-process edge-smoothing techniques have been developed, such as MLAA (used in Killzone 3 and Dragon Age 2, among others), FXAA (used in Crysis 2, FEAR 3, Duke Nukem Forever), SRAA, DLAA (used in Star Wars: The Force Unleashed II), post MSAA (used in Crysis 2 as default anti-aliasing solution). Another popular technique is Temporal anti-aliasing, used in Halo Reach. DirectX 10 introduced features allowing shaders to access individual samples in multisampled render targets (and depth buffers in version 10.1), making hardware anti-aliasing possible in deferred shading. These features also make it possible to correctly apply HDR luminance mapping to anti-aliased edges, where in earlier hardware any benefit of anti-aliasing may be lost, making this form of anti-aliasing desirable in any case.